The objective of this proposal is to study the role of macrophages, thymus (T)-, and bone marrow (B)-derived cells in sensitization to and rejection of tumor transplants. Mouse lymphoid cells (T- and B-cells) will be exposed for 3 hrs in vitro, to transplantation antigens provided by an allogeneic macrophage or tumor monolayer, or to tumor specific transplantation antigens, provided by a syngeneic tumor monolayer. The in vitro sensitized cells will be assayed, by their ability to reject, in accelerated fashion, in vivo tumor transplants. The role of T- and B-cells during in vitro sensitization and in vivo graft rejection will be determined by incubating the lymphoid cells both before and after in vitro sensitization with anti-T cell (anti-theta), or anti-B cell (anti-beta) serum. The role of the macrophages will be determined by pretreating lymphoid cells with anti-macrophage serum and testing the ability of these cells to become sensitized in vitro to tumor cell antigens. The results will tell us whether macrophages, T- and B-cells are required for the in vitro sensitization to tumor antigens and whether, after sensitization, one cell type can accomplish tumor graft destruction.